Compared with the conventional flat-panel display technique, the electrophoretic display shows low energy consumption, flexibility, high contrast ratio, high image bistability, good visibility and simple application. With the advantage of conventional paper and electron display, the electrophoretic display technique is one of the most promising approaches for current electronic paper applications. Electrophoretic display technique was proposed in the 1970s, which attracted extensive attention gradually. As the core component of electrophoretic display, electrophoretic display medium has direct influences on the effect and performance of electrophoretic display. In 1970, Matsushita Electric Industrial Co. issued a patent U.S. Pat. No. 3,892,568, which disclosed a preparation process of electrophoretic display material which contained at least one type of electrophoretic particles. In 1989, Nippon Mektron Ltd. Issued a patent JP1086116, which disclosed an electrophoretic display system with the encapsulated electrophoretic display medium which contained at least one type of electrophoretic particles. In 1997, E ink Co. issued a patent U.S. Pat. No. 6,120,588, which disclosed a type of electrophoretic display unit composed of encapsulated electrophoretic display medium which contained two types of charged pigment particles. However, this type of electrophoretic display unit has the disadvantages as below:                1. In electrophoretic display medium, the positively charged and negatively charged pigment particles are attracted to each other. As a result, it causes aggregation and sediment of the pigment particles.        2. It involves a complicated surface treatment of the charged pigment particles.        3. The preparation process of the electrophoretic display medium is complicated.        
Therefore, these disadvantages lead to low bistability, low chroma, decreased brightness of colors, low contrast ratio, low repeatability of the performance of electrophoretic display medium.